Olefins are unsaturated open hydrocarbons, i.e., hydrocarbons having at least some double or triple carbon-to-carbon bonds. Examples of olefins having double carbon-to-carbon bond include ethylene (C2H4) and propylene (C3H6). Acetylene (C2H2) is an example of an olefin having a triple carbon-to-carbon bond. Conventional methods for manufacturing olefins include cracking from crude oil. For example, longer hydrocarbon chains having single carbon-to-carbon bonds (i.e., saturated hydrocarbons) and/or cyclical hydrocarbons can be synthesized into shorter hydrocarbon chains with double carbon-to-carbon bonds under high temperatures in presence of steam. The temperature needed to sustain this reaction may reach 1200 K. Additionally, the conventional cracking process requires good process control because if the product temperature or residence time is excessive, undesired carbon deposits may form on the equipment. Conversely, if the product temperature is too low or residence time is too short, the conversion to the olefins is incomplete, thereby reducing the efficiency of the cracking.
FIG. 1 illustrates a shock wave olefin reactor 100 configured in accordance with the prior art and the accompanying temperature graph of the gases in the reactor. The shock wave reactor 100 is suitable for manufacturing olefins by synthesizing feedstock gas (e.g., removing the hydrogen atoms from the feedstock gas). In the illustrated process, a high temperature carrier gas (e.g., steam at temperature Tco) is fed at an entrance 115 of a subsonic section 110. A feedstock gas 120 (e.g., having hydrocarbons with single carbon-to-carbon bonds or methane (CH4)) is added at some downstream distance from the entrance 115 through nozzles 121 at temperature Tfo that is smaller than Tco. A mixture of carrier gas and feedstock gas expands and accelerates through a diffuser section 125. The carrier gas 115 and the feedstock gas 120 further mix as they travel through a mixing section 130 toward a shock wave location 135. Upstream of the shock wave location 135, flow of the carrier gas/feedstock gas mixture is supersonic, while the flow of the carrier gas/feedstock gas mixture downstream of the shock wave location 135 is subsonic. The transition from supersonic conditions (T2, M2) to subsonic conditions (T3, M3) is accompanied by a rapid temperature rise in the mixture, which promotes conversion from methane and/or the hydrocarbons having single carbon-to-carbon bonds to hydrocarbons having at least some double or triple carbon-to-carbon bonds. The hydrocarbons continue to rapidly react in a section 145 downstream of the shock wave location 135 due to a relatively high temperature in this section. Further downstream, the olefins enter a heat exchanger 150 where they are cooled down to a lower temperature. The olefins, the remaining unreacted hydrocarbons, and other products of reaction (e.g., carrier gas, carbon) exit the reactor 100 at an outlet 155 as a stream 160.
This conventional process, however, suffers from several shortcomings. For example, the nozzles 121 in the stream of carrier gas can overheat and can also cause undesirable pressure losses in the carrier gas. Mixing of the feedstock gas and the carrier gas may be incomplete when the mixture arrives to the shock wave location 135. Furthermore, rapid temperature increase across the shock wave location 135 is difficult to control and may cause overheating or underheating of the feedstock gas. Such overheating/underheating may result in carbonization or incomplete reaction of the feedstock gases.